The present invention relates to an echo canceler and, more particularly, to an echo canceler suitable for a packet data signal.
Generally, to cancel an echo, an echo canceller generates a false echo component by referencing a received signal, and then subtracts the false echo component from a signal to be transmitted. A signal remaining in the signal undergone echo cancellation, i.e., a residual echo signal is used to update the filter coefficients of an adaptive FIR (Finite Impulse Response) filter for echo estimation. As a result, the residual echo signal is brought close to zero.
A conventional echo canceller for packet data signals includes a receive buffer for converting the rate of a packet data signal to be input to an FIR filter to a preselected rate. On the other hand, a received signal is reflected by a four-wire/two-wire converter and introduced into the signal to be transmitted as an echo component. In light of this, the echo canceller further includes a transmit buffer for converting the rate of the packet signal to be transmitted to a preselected rate. If the rate of the packet data signal or burst signal is not converted, then the filter will be required to have an extremely high-speed computation capability and will thereby make it difficult to implement the hardware of the echo canceller.
The FIR filter for estimating an echo by the above signal rate conversion can be implemented with the conventional processing speed. However, a delay ascribable to the signal rate conversion inevitably occurs between the input and the output of a transmission line on which echo cancellation is effected, aggravating a channel delay.